Low temperature adhesive resins for wafer bonding

ABSTRACT

A method for adhesive bonding in microelectronic device processing is provided that includes bonding a handling wafer to a front side of a device wafer with an adhesive comprising phenoxy resin; and thinning the device wafer from the backside of the device wafer while the device wafer is adhesively engaged to the handling wafer. After the device wafer has been thinned, the adhesive comprising phenoxy resin may be removed by laser debonding, wherein the device wafer is separated from the handling wafer.

BACKGROUND

Technical Field

The present disclosure relates generally to adhesives employed in waferbonding.

Description of the Related Art

Temporary wafer bonding/debonding is an important technology forimplementing the fabrication of semiconductor devices, photovoltaicdevices, and electrical devices of micron and nanoscale. Bonding is theact of attaching a device wafer, which is to become a layer in a finalelectronic device structure, to a substrate or handling wafer so that itcan be processed, for example, with wiring, pads, and joiningmetallurgy. Debonding is the act of removing the processed device waferfrom the substrate or handling wafer so that the processed device wafermay be employed into an electronic device. Some existing approaches fortemporary wafer bonding/debonding involve the use of an adhesive layerplaced directly between the silicon device wafer and the handling wafer.When the processing of the silicon device wafer is complete, the silicondevice wafer may be released from the handling wafer by varioustechniques, such as by exposing the wafer pair to chemical solventsdelivered by perforations in the handler, by mechanical peeling from anedge initiation point or by heating the adhesive so that it may loosento the point where the silicon device wafer may be removed by sheering.

SUMMARY

In one embodiment, a method for adhesive bonding in microelectronicdevice processing is provided that includes bonding a handling wafer toa front side surface of a device wafer with an adhesive comprisingphenoxy resin; and thinning the device wafer from the backside surfaceof the device wafer while the device wafer is adhesively engaged to thehandling wafer. After the device wafer has been thinned, the adhesivecomprising phenoxy resin may be removed by laser debonding, wherein thedevice wafer is separated from the handling wafer.

In another embodiment, the method of adhesive bonding may includebonding a handling wafer to a front side of a device wafer with anadhesive comprising phenoxy resin, wherein the adhesive is cured at atemperature of less than 300° C. The cured phenoxy resin may have aviscosity greater than 1×10⁵ Pa·Sec. Following bonding of the handlingwafer to the device wafer, the device wafer may be thinned from thebackside surface of the device wafer, while the device wafer isadhesively engaged to the handling wafer. After the device wafer hasbeen thinned, the adhesive comprising phenoxy resin may be removed,wherein the device wafer is separated from the handling wafer.

In another embodiment, a method of adhesive bonding is provided that mayinclude bonding a first semiconductor substrate to a secondsemiconductor substrate with an adhesive comprising phenoxy resin,wherein the adhesive is cured at a temperature of less than 300° C. Thecured phenoxy resin may have a viscosity greater than 1×10⁵ Pa·Sec.

BRIEF DESCRIPTION OF DRAWINGS

The disclosure will provide details in the following description ofpreferred embodiments with reference to the following figures wherein:

FIG. 1 is a side cross-sectional view of a semiconductor substrate thatmay be employed as a device wafer in a method of forming a semiconductordevice that employs adhesive bonding of the device wafer to a handlingwafer as part of a wafer thinning sequence, in accordance with thepresent disclosure.

FIG. 2 is a side cross-sectional view of forming semiconductor deviceson a front surface of the device wafer, in accordance with oneembodiment of the present disclosure.

FIG. 3 is a side cross-sectional view of bonding a handling wafer to thefront surface of the device wafer through an adhesive containing phenoxyresin, in accordance with one embodiment of the present disclosure.

FIG. 4 is a side cross-sectional view depicting thinning the backsidesurface of the device wafer, in accordance with one embodiment of thepresent disclosure.

FIG. 5 is a side cross-sectional view depicting patterning the backsidesurface of the thinned device wafer, in accordance with one embodimentof the present disclosure.

FIG. 6 is a side cross-sectional view depicting laser debonding toablate the adhesive containing phenoxy resin, and to remove the handlingwafer from the device wafer, in accordance with one embodiment of thepresent disclosure.

FIG. 7 is a plot illustrating the viscosity of typical adhesives, suchas poly(meth)acrylate adhesives, as a function of temperature.

FIG. 8 is a plot illustrating a comparison of the viscosity of adhesivescontaining phenoxy resin in comparison to poly(meth)acrylate adhesivesover a temperature range of approximately 160° C. to 210° C.

FIG. 9 is a plot illustrating a comparison of the viscosity of adhesivescontaining phenoxy resin in comparison to poly(meth)acrylate adhesivesover a temperature range of approximately 40° C. to 210° C.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Detailed embodiments of the claimed structures and methods are disclosedherein; however, it is to be understood that the disclosed embodimentsare merely illustrative of the claimed structures and methods that maybe embodied in various forms. In addition, each of the examples given inconnection with the various embodiments are intended to be illustrative,and not restrictive. Further, the figures are not necessarily to scale,some features may be exaggerated to show details of particularcomponents. Therefore, specific structural and functional detailsdisclosed herein are not to be interpreted as limiting, but merely as arepresentative basis for teaching one skilled in the art to variouslyemploy the methods and structures of the present disclosure. Referencein the specification to “one embodiment” or “an embodiment” of thepresent principles, as well as other variations thereof, means that aparticular feature, structure, characteristic, and so forth described inconnection with the embodiment is included in at least one embodiment ofthe present principles. Thus, the appearances of the phrase “in oneembodiment” or “in an embodiment”, as well any other variations,appearing in various places throughout the specification are notnecessarily all referring to the same embodiment.

For purposes of the description hereinafter, the terms “upper”, “lower”,“right”, “left”, “vertical”, “horizontal”, “top”, “bottom”, andderivatives thereof shall relate to the embodiments of the disclosure,as it is oriented in the drawing figures. The term “positioned on” meansthat a first element, such as a first structure, is present on a secondelement, such as a second structure, wherein intervening elements, suchas an interface structure, e.g. interface layer, may be present betweenthe first element and the second element. The term “direct contact”means that a first element, such as a first structure, and a secondelement, such as a second structure, are connected without anyintermediary conducting, insulating or semiconductor layers at theinterface of the two elements.

In some embodiments, the methods, compositions and structures disclosedherein provide low cost, thermoplastic materials that can be used asadhesives in temporary bonding of thin layers of semiconductor material,such as silicon containing material layers, to wafer handler substrates.As used herein, the term “thin” denotes a thickness of 5 microns to 10microns. In some embodiments, the methods, compositions and structuresdisclosed herein provide an adhesive that can be used in method thatemploy laser debonding. Laser debonding is one method that is typicallyemployed in layer transfer techniques used in microelectronicproduction, such as the formation of microelectronics employingsilicon-containing substrates.

Typically, in laser debonding, a polyimide material is used as theadhesive connecting the device wafer to a handling wafer, whereinablating the polyimide adhesive employs a deep UV excimer laser thatdebonds the device wafer from the handling wafer. The handling wafer maybe a coefficient of thermal expansion (CTE) matched glass plate. In someexamples, the polyimide that is used as the adhesive is known in theindustry by tradename HD3007, which may be available from HDMicrosystems, Inc. It has been determined that one disadvantage of usinga polyimide adhesive material as the adhesive in wafer bonding methodsin microelectronics device manufacturing is the relatively highprocessing temperature that is required to convert the polyimideprecursor, i.e., polyamic acid, to a fully imidized polyimide beforecompleting bonding of the handling wafer to the device wafer. Thetemperature range that is typically used to cure the polyimide toprovide imidization ranges 300° C. to 400° C. In addition, the nature ofa polyimide polymer is usually relatively stiff and rigid such that thepolymer requires a high temperature to soften and bond to the handlingwafer. The high temperatures required for both steps can do damage tosensitive devices that are included in the device wafer. Further, thehigh temperatures required for curing the polyimide for imidization andto soften the polyimide for softening can cause stresses in the devicewafer that induce warping in the device wafer after cooling.Additionally, in order to remove polyimide residues that remain afterdebonding long soak times in strong hot solvents, such asN-methylpyrrolidone (NMP) and dimethyl sulfoxide (DMSO), may berequired.

Adhesives composed of poly (meth)acrylates that do not require hightemperatures to imidize or bond and that use less aggressive removingsolvents, such as those available from Tokyo Ohka Kogyo Co. (TOK) andBrewer Science, are too costly and have too low a viscosity duringbonding above 170° C. This low viscosity at temperatures greater than170° C. can cause ‘squeeze out’ of adhesive material at bonding temps ofapproximately 200° C. to 210° C.

In some embodiments, the methods, structures and compositions providedherein provide a set of resins that are low cost and have beendetermined to have good bond/debonding performance for adhesives atlower temperatures than polyimides without exhibiting squeeze-outphenomena. In some embodiments, the present disclosure provides a methodof adhesive bonding that may include bonding a first semiconductorsubstrate to a second semiconductor substrate with an adhesivecomprising phenoxy resin, wherein the adhesive is cured at a temperatureof less than 300° C. The cured phenoxy resin may have a viscositygreater than 1×10⁵ Pa·Sec.

As used herein, the term “phenoxy resin” denotes a family of BisphenolA/epichlorohydrin linear polymers. Phenoxy resins are typically toughand ductile thermoplastic materials having high cohesive strength andgood impact resistance. The backbone ether linkages and pendant hydroxylgroups promote wetting and bonding to polar substrates. Structurally, insome examples, the phenoxy resin may be polyhydroxyether having terminalalpha-glycol groups. In some embodiments, weight-average molecularweights for the phenoxy resins in accordance with the present disclosuremay range from approximately 25,000 to above 60,000. The highestpolymeric species of phenoxy resin may exceed 250,000 daltons.olydispersity is very narrow, typically less than 4.0. An averagemolecule contains 40 or more regularly spaced hydroxyl groups. Thephenoxy resin may be a thermoplastic resin suitable for use as anadhesive in low temperature, e.g., less than 300° C., wafer bondingand/or laser debonding applications.

In some embodiment of the present disclosure, the phenoxy resin is aPhenoxy Resin PKHC®, PKHH® or PKHJ® having the following formula:

PKHH is available from InChem Corp., in which PKHH phenoxy resin has theIUPAC name: 2-(chloromethyl)oxirane;4-[2-(4-hydroxyphenyl)propan-2-yl]phenol, and chemical formulaC₁₈H₂₁ClO₃. PKHJ and PKHC are also available from InChem Corp. PKHHphenoxy resin has a molecular weight of approximately 52,0000 Mw/13,000Mn (avg.), and has a viscosity ranging from 180-280 cP (Brookfield @ 25°C. 20% in cyclohexanone). PKHJ phenoxy resin may have a molecular weightof approximately 57,0000 Mw/16,000 Mn (avg.), and has a viscosityranging from 600-775 cP (Brookfield @ 25° C. 20% in cyclohexanone). PKHCphenoxy resin may have a molecular weight of approximately 43,0000Mw/11,000 Mn (avg.), and has a viscosity ranging from 410-524 cP(Brookfield @ 25° C. 20% in cyclohexanone).

In some embodiments, the phenoxy resin adhesive may be a phenoxy resinthat is modified with a dye. In some embodiments, the present disclosureprovides for covalently reacting hydroxyl functional adhesive polymerswith appropriately reactive dye molecules to permanently attach the dyefor ease of recycling. For example, the hydroxyl groups of the phenoxyresin may be esterified with acid functional molecules. For example, thephenoxy resin may be modified, e.g., esterified, with 9-anthracenecarboxylic acid. In another example, the phenoxy resin may be modified,e.g., esterified, with 2-anthraquinon carboxylic acid. It is noted thatthe above examples are provided for illustrative purposes only, as otherdyes, e.g., other carboxylic acid containing molecules, may be used tomodify the phenoxy resin. For example, other hydroxyl reactive materialsare available and useful also for dye attachment such as isocyanate,chloromethyl, chlorosulfonyl and combinations thereof. A covalentlybonded dye, as described above can be used to both collect and reuseadhesive that is washed off of a device wafer following its use.

The phenoxy resin adhesives disclosed herein may be used in anylayer/substrate transfer and/or substrate bonding method used forforming semiconductor devices, memory devices, photovoltaic devices,microelectronic devices and nanoscale devices. For example, the phenoxyresin adhesives may be used in process that employ mechanical spalling,such as the method described in U.S. Pat. No. 8,247,261 titled “THINSUBSTRATE FABRICATION USING STRESS INDUCED SUBSTRATE SPALLING”. Thephenoxy resin may also be used as a bonding adhesives in methods forforming III-V semiconductor containing semiconductor devices andphotovoltaic devices that include a reusable germanium (Ge) containingsubstrate as a growth surface. In this example, once the III-V device isformed it is bonded to a supporting substrate, and the reusablegermanium (Ge) containing substrate is removed from the III-V device tobe used as the growth surface for forming another device. The phenoxyresins may also be used in layer transfer processes that employ smartcut to separate a portion of a material layer for transfer to asupporting substrate. Smart cut may include implanting a dopant species,such as hydrogen, into a material layer to provide a weakened interfaceacross when the material layer is to be cleaved. A portion of thecleaved material layer may be adhesively bonded to a supportingsubstrate using the phenoxy resins. In other embodiments, the phenoxyresin may be employed in a substrate, i.e., device wafer, thinningprocess. It is noted that the above examples of adhesive applicationsfor the phenoxy resin is provided for illustrative purposes only, and isnot intended to limit the present disclosure. Further details of themethods and structures of the present disclosure that employ a phenoxyresin as a bonding adhesive as part of a method sequence for formingsemiconductor devices that includes wafer thinning and debonding of ahandling wafer are now discussed with greater detail with reference toFIGS. 1-6.

FIG. 1 depicts one embodiment of a device wafer 5, e.g., semiconductorsubstrate, that may be employed in at least one embodiment of thepresent disclosure. In some embodiments, the device wafer 5 may beprovided by a bulk semiconductor substrate. The bulk semiconductorsubstrate may have a single crystal, i.e., monocrystalline, crystalstructure. In some embodiments, the device wafer 5 is composed of asilicon including material. In some embodiments, the silicon includingmaterial that provides the device wafer 5 may include, but is notlimited to silicon, single crystal silicon, multicrystalline silicon,polycrystalline silicon, amorphous silicon, strained silicon, silicondoped with carbon (Si:C), silicon alloys or any combination thereof. Inother embodiments, the device wafer 5 may be a semiconducting materialthat may include, but is not limited to, germanium (Ge), silicongermanium (SiGe), silicon germanium doped with carbon (SiGe:C),germanium alloys, GaAs, InAs, InP as well as other III/V and II/VIcompound semiconductors. The thickness T1 of the device wafer 5 mayrange from 10 microns to a few millimeters.

FIG. 2 depicts forming semiconductor devices 10 on a front surface 15 ofthe device wafer 5. As used herein, “semiconductor device” refers to anintrinsic semiconductor material that has been doped, that is, intowhich a doping agent has been introduced, giving it different electricalproperties than the intrinsic semiconductor. In some embodiments, thesemiconductor devices 10 are field effect transistors (FETs). A fieldeffect transistor (FET) is a transistor in which output current, i.e.,source-drain current, is controlled by the voltage applied to the gate.A field effect transistor typically has three terminals, i.e., gate,source and drain. The semiconductor devices 10 that may be formed usingthe methods of the present disclosure are applied to may be planarsemiconductor devices, FinFETS, Trigate semiconductor devices, nanowiresemiconductor devices or a combination thereof. The semiconductordevices 10 disclosed herein may also be provided by memory devices,e.g., flash memory or eDRAM memory.

In some embodiments, the semiconductor devices 10 may include a gatestructure 11 that includes at least one gate dielectric 12, at least onegate conductor 13 and at least one gate sidewall spacer 14.

The at least one gate dielectric 12 may be a dielectric material, suchas SiO₂, or alternatively high-k dielectrics, such as oxides of Ta, Zr,Al or combinations thereof. In another embodiment, the at least one gatedielectric 12 is comprised of an oxide, such as SiO₂, ZrO₂, Ta₂O₅ orAl₂O₃. In one embodiment, the at least one gate dielectric 12 may have athickness ranging from 1 nm to 10 nm.

The at least one gate conductor layer 13 may include a metal gateelectrode. The metal gate electrode may be any conductive metalincluding, but not limited to W, Ni, Ti, Mo, Ta, Cu, Pt, Ag, Au, Ru, Jr,Rh, and Re, and alloys that include at least one of the aforementionedconductive elemental metals. In other embodiments, the at least one gateconductor 13 may include a doped semiconductor material, such as a dopedsilicon containing material, e.g., doped polysilicon.

In some embodiments, a gate dielectric (not shown) may be present atopthe at least one gate conductor 13. The at least one gate dielectric capmay be composed of an oxide or nitride material.

Each of the material layers for the gate dielectric cap, the at leastone gate conductor layer 13, and the gate dielectric layer 12 may beformed using a deposition or growth process. For example, the gatedielectric layer 12 and the gate dielectric cap may be formed using achemical vapor deposition (CVD) process, such as plasma enhanced CVD(PECVD). The gate conductor layer 13 may be formed using a physicalvapor deposition (PVD) process, e.g., sputtering, when the gateconductor layer 13 is composed of a metal, or the gate conductor layer13 may be formed using a chemical vapor deposition (CVD) process whenthe gate conductor layer 3 is composed of a doped semiconductormaterial, e.g., polysilicon.

Following formation of the gate stack, the stack of material layers arepatterned and etched. Specifically, a pattern is produced by applying aphotoresist to the surface of the gate stack to be etched, exposing thephotoresist to a pattern of radiation, and then developing the patterninto the photoresist utilizing a resist developer. Once the patterningof the photoresist is completed, the sections covered by the photoresistare protected while the exposed regions are removed using a selectiveetching process that removes the unprotected regions. The etch processfor removing the exposed portions of the gate stack may be ananisotropic etch. As used herein, an “anisotropic etch process” denotesa material removal process in which the etch rate in the directionnormal to the surface to be etched is greater than in the directionparallel to the surface to be etched.

The anisotropic etch process may be provided by reactive ion etch.Reactive Ion Etching (RIE) is a form of plasma etching in which duringetching the surface to be etched is placed on the RF powered electrode.Moreover, during RIE the surface to be etched takes on a potential thataccelerates the etching species extracted from plasma toward thesurface, in which the chemical etching reaction is taking place in thedirection normal to the surface.

A gate sidewall spacer 14 can be formed in direct contact with thesidewalls of the gate stack. The gate sidewall spacers 14 are typicallynarrow having a width ranging from 2.0 nm to 15.0 nm. The gate sidewallspacer 14 can be formed using deposition and etch processing steps. Thegate sidewall spacer 14 may be composed of a dielectric, such asnitride, oxide, oxynitride, or a combination thereof.

FIG. 2 also depicts one embodiment of forming source and drain regions16, 17 on the opposing sides of the gate structure 11. As used herein,the term “drain” means a doped region in a semiconductor substrate thatis located at the end of the channel in field effect transistors (FET),in which carriers are flowing out of the transistor through the drain.As used herein, the term “source” is a doped region from which majoritycarriers are flowing into the channel. The source and drain regions16,17 may be formed by ion implanting an n-type or p-type dopant intothe device wafer 5. As used herein, “p-type” refers to the addition ofimpurities to an intrinsic semiconductor that creates deficiencies ofvalence electrons. In a type IV semiconductor, such as silicon (Si),examples of n-type dopants, i.e., impurities, include but are notlimited to: boron, aluminum, gallium and indium. As used herein,“n-type” refers to the addition of impurities that contributes freeelectrons to an intrinsic semiconductor. In a type IV semiconductor,such as silicon (Si), examples of n-type dopants, i.e., impurities,include but are not limited to antimony, arsenic and phosphorous.Typically, the conductivity type, i.e., n-type or p-type conductivity,for the source and drain regions 16, 17 is the conductivity type of thesemiconductor device, e.g., n-type field effect transistor (nFET) orp-type field effect transistor (pFET).

In some embodiments, multiple semiconductor devices 10 are formed on thefront side surface 15 of the device wafer 5, wherein the multiplesemiconductor devices 10 may include a first set of first conductivitytype semiconductor, e.g., n-type FET, and a second set a secondconductivity type, e.g., p-type FET. Isolation regions 18, such astrench isolation regions may be formed separating semiconductor devicesof different conductivity types, e.g., electrically isolated p-type FETSfrom n-type FETS. For example, lithography, etching and filling of thetrench with a trench dielectric may be used in forming the trenchisolation region. The trench isolation region may be composed of anoxide, such as silicon oxide.

FIG. 3 depicts bonding a handling wafer 25 to the front side surface 15of the device wafer 5 through an adhesive layer 20 containing phenoxyresin. The adhesive layer 20 may be composed of any of the phenoxy resincompositions that have been described above including, but not limitedto, Phenoxy Resin PKHC®, PKHH® or PKHJ® available from InChem Corp. Inone example, the adhesive layer may be a phenoxy resin having thechemical name:polyoxy(2-hydrozy-1,3-propanediyl)oxy-1,4-phenylene(1-methylethylidene)-1,4-phenylene.

FIG. 3 depicts the device wafer 5 is bonded onto the handling wafer 25creating a compound wafer. The bonding process should be compatible withthe properties of the device wafer 5, such as surface topography,surface material, restrictions in process temperature, and combinationsthereof. In some examples, the temporary adhesive, i.e., adhesive layer20 containing phenoxy resin, provides a planar surface to the topographyof the device wafer 5, and establishes a void free bond interface forbonding to the handling wafer 25.

The adhesion layer 20 may be applied to the front side surface 15 of thedevice wafer 5 covering the semiconductor devices 10 using a depositionprocess, such as spin coating. Typical spin solvents that are suitablefor depositing the adhesion layer 20 using spin coating may includePropylene Glycol Methyl Ether (PGME), Propylene glycol monomethyl etheracetate (PGMEA), ethyl lactate, N-Methyl-2-pyrrolidone (NMP) andcombinations thereof. In some embodiments, the spin coating solution mayfurther include cyclohexanone.

One example of a spin coating apparatus for depositing the adhesivelayer 20 is a fully automated coater system ACS200 from SUSS MicroTec.In one example, a center dispense of the liquid material may be employedfollowed by a spread spin at 1000 rpm for 10 seconds. After the spreadspin, the material was spun off at 1400 rpm for 60 seconds. It is notedthat the above described coating process is only one example of a methodof depositing the adhesion layer 20 on the front surface of the devicewafer 5, and that other deposition methods may be suitable for applyingthe adhesion layer 20. For example, the adhesion layer 20 may bedeposited using spraying, brushing, curtain coating and dip coating.

Following application of the adhesive layer 20 to the front side surface15 of the device wafer 5, a handling wafer 25 is contacted to thesurface of the adhesive layer 20 that is opposite the surface of theadhesive layer 20 under temperature and pressure to provide that thehandling wafer 25 is bonded to the device wafer 5 through the adhesivelayer 20. In some embodiments, the thickness T2 of the adhesive layer 20between the handling wafer 25 and the device wafer 5 may range from 2microns to 10 microns. In other embodiments, the thickness T2 of theadhesive layer 20 may range from 2 microns to 5 microns.

The handling wafer 25 may be composed of a material and thickness tostructurally support the device wafer 5 without warping or crackingduring subsequent thinning steps, such as planarization and/or grinding.In one embodiment, the handling wafer 25 is composed of glass. In someembodiments, the material of the handling wafer is selected to have acoefficient of thermal expansion (CTE) that is similar to the CTE of thedevice wafer 5 to avoid any disadvantageous mechanical effects that canresult from two materials engaged to one another having differentthermal expansion coefficients, such as warping. In some embodiments, aglass handling wafer 25 may be advantageous to provide for transmissionof the laser signal through the glass handling wafer 25 duringsubsequent laser debonding steps. In other embodiments, the handlingwafer 25 may be composed of a metal material or a dielectric material.In some embodiments, the glass handling wafer 25 can be composed of asemiconductor material. For example, the above examples of semiconductormaterials for the device wafer 25 are equally suitable for thesemiconductor materials for the handling wafer 25.

To provide bonding, temperature and pressure was applied to thecomposite of the handling wafer 25, the adhesion layer 20 and the devicewafer. In one embodiment, the bonding temperature may range between 150°C. to 250° C., and the pressure applied may range from 0.07 MPA to 0.22MPa. In another embodiment, the bonding temperature may range from 175°C. to 200° C., and the pressure may range from 0.15 MPa to 0.22 MPa. Thetime period at which the bonding temperature and pressure is held mayrange from 10 minutes to 60 minutes. The bonding step may be performedin a nitrogen atmosphere.

Typically, bonding includes elevating the temperature of the adhesionlayer 20 of the phenoxy resin to effectuate curing of the polymer. Insome embodiments, a phenoxy resin adhesive, such aspolyoxy(2-hydrozy-1,3-propanediyl)oxy-1,4-phenylene(1-methylethylidene)-1,4-phenylene,has a viscosity ranging from 100-10,000 Pa·seconds when at a temperatureranging from 160° C. to 210° C., and under a pressure of 1000 mbar perarea of an 8 inch wafer size for at least one of the device wafer 5and/or handing wafer 20. The viscosity of the phenoxy resin adhesive isat least one order of magnitude greater than typical adhesives composedof polyimides and/or poly(meth)acrylates. In prior adhesives, such aspolyimide and/or poly(meth)acrylates bonding at temperatures below 300°C. resulted in too low a viscosity of the adhesive layer, which resultedin adhesive squeeze out. By providing a higher viscosity with phenoxyresin adhesives, squeeze out of the adhesive layer 20 during bonding ofthe handling wafer 25 to the device wafer 20 is substantially reduced ifnot eliminated. In some embodiments, the viscosity of the phenoxy resinat temperatures ranging from 160° C. to 210° C. may range from1,500-10,000 Pa·second. In another embodiment, the viscosity of thephenoxy resin at temperatures ranging from 160° C. to 210° C. may rangefrom 2500-10,000 Pa·second. In yet another embodiment, the viscosity ofthe phenoxy resin at temperatures ranging from 160° C. to 210° C. mayrange from 5000-10,000 Pa·second. In one examples, the viscosity of thephenoxyl resin at temperatures ranging from 160° C. to 210° C. may beequal to 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1500, 2000,2500, 3000, 3500, 4000, 4500, 5000, 5500, 6000, 6500, 7000, 7500, 8000,8500, 9000, 9500, and 10000 Pa·second, and any range including at leasttwo of the above noted values.

The adhesion layer 20 following bonding to the handling wafer 25 and thedevice substrate 5 may have a shear strength of 40 MPa or greater.

Another advantage of the present methods is that the curing of thephenoxy resin is at temperatures less than the curing temperatures thatare required of prior adhesives, such as polyimides and/orpoly(meth)acrylates. For example, imidization of polyimides requirestemperatures greater than 300° C., which results in damage to the devicewafer, such a wafer warpage and/or cracking. Additionally, the hightemperatures required of prior adhesives composed of polyimides and/orpoly(meth)acrylates may also result in unnecessary out diffusion of thedopants of the semiconductor devices that have been integrated into thedevice wafer 5. Bonding with phenoxy resin is at temperatures below 300°C., which is at a temperature that does not damage, i.e., does not causewarping or cracking of the device wafer 5, and does not causeoutdiffusion of the semiconductor device dopants. In one embodiment, thebonding temperature of the phenoxy resin adhesive may range from 150° C.to 290° C. In another embodiment, the bonding temperature of the phenoxyresin adhesive may range from 160° C. to 210° C. In other examples, thebonding temperature of the phenoxy resin may be at 150, 160, 170, 180,190, 200, 210, 220, 240, 250, 260, 270, 280 and 290° C., as well as anyrange including two of the aforementioned values.

In some embodiments, the phoxyl resin adhesive that provides theadhesion layer 20 is not susceptiable to degredation by exposure to thefollowing sovlents: acetone, NMP, 6N HCl, 15% H₂O₂, 30% NH₄OH, 10% Kl inH₂O, EtOH, MeOH, Isopropyl Alcohol (IPA), cyclohexanone, ethyl lactate,PGMEA, PGME, 30% HCl, 70% HNO₃ and combinations thereof.

FIG. 4 depicting thinning the backside surface 26 of the device wafer 5.The device wafer 5 may be thinned by applying a planarization processand/or a grinding process to the backside surface 26 of the device wafer5. In one example, the planarization and grinding process may beprovided by chemical mechanical planarization (CMP). In an alternativeembodiment, etch processes may be used to remove material from the backsurface 26 of the device wafer 5. Following thinning of the backsidesurface 26 of the device wafer 5, the thinned device wafer 5 may have athickness T3 ranging from 5 microns to 100 microns. In anotherembodiment, the thinned device wafer 5 may have a thickness T3 rangingfrom 20 microns to 50 microns. In one example, the thinned device wafer5 may have a thickness T3 ranging from 5 microns to 10 microns. Thehandling wafer 25 supports the device wafer 5 during the mechanicalthinning process to protect the device wafer 5 from mechanical failure,such as cracking.

FIG. 5 depicting one example of patterning the backside surface 26 ofthe thinned device wafer 5. The patterning step depicted in FIG. 5 maybe employed to form interconnects to the semiconductor devices 10 thatare integrated within the device wafer 5. For example, via interconnects30, such as through silica vias (TSV), may be formed to the activeregions of the device wafer 5. Through silica vias (TSV) may be employedto interconnect stacked devices wafers in forming a three dimensional(3D) microelectronic device. Vias can be formed to the active portionsof the semiconductor devices, e.g., source and drain regions 16, 17,using photoresist deposition, lithographic patterning to form aphotoresist etch mask, and etching, e.g., anisotropic etching. Followingvia formation, via interconnects 30 are formed by depositing aconductive metal into the via holes using deposition methods, such asCVD, sputtering or plating. The conductive metal may include, but is notlimited to: tungsten, copper, aluminum, silver, gold and alloys thereof.

FIG. 6 depicts one embodiment of debonding the handling wafer 25 fromthe device wafer 5. In one embodiment, debonding of the handling wafer25 may include laser debonding to ablate the adhesion layer 20containing the phenoxy resin, and to remove the handling wafer 25 fromthe device wafer 5. Laser debonding may be provided by a 200 nm or 308nm excimer laser. The UV laser may function using a cold process. Forexample, a 308 nm ultraviolet light emitted by the excimer laser isabsorbed near the interface between the device wafer 5 and the glasshandling wafer 25, penetrating only a few hundred nanometers. Thus,leaving the device wafer 5 unaffected. Furthermore, the ultravioletlight from the excimer laser debonds through primarily a photochemicalmeans, by directly breaking chemical bonds in the adhesion layer 20 ofphenoxy resin. The excimer laser may be applied in line mode, or stepand repeat mode. The non-thermal process breaks down the temporaryadhesive at the adhesion layer 20 and glass handling wafer 25 interface.Following application of the excimer layer, the handling wafer 35 may belifted and carried away from the device wafer 5.

In some embodiments, phenoxy resin residues following removal of theadhesion layer 25 may be removed using a solvent selected from the groupconsisting of gamma-butyrolactone, ethyl lactate, other lactate isomersknown under the tradename Gavesolv, NMP, Tetrahydrofuran (THF),PMAcetate, Methyl isobutyl ketone (MIBK), Methyl ethyl ketone (MEK), andcombinations thereof.

Methods as described herein may be used in the fabrication of integratedcircuit chips. The resulting integrated circuit chips can be distributedby the fabricator in raw wafer form (that is, as a single wafer that hasmultiple unpackaged chips), as a bare die, or in a packaged form. In thelatter case the chip is mounted in a single chip package (such as aplastic carrier, with leads that are affixed to a motherboard or otherhigher level carrier) or in a multichip package (such as a ceramiccarrier that has either or both surface interconnections or buriedinterconnections). In any case the chip is then integrated with otherchips, discrete circuit elements, and/or other signal processing devicesas part of either (a) an intermediate product, such as a motherboard, or(b) an end product. The end product can be any product that includesintegrated circuit chips, ranging from toys and other low-endapplications to advanced computer products having a display, a keyboardor other input device, and a central processor.

The following examples are provided to further illustrate the presentdisclosure and demonstrate some advantages that arise therefrom. It isnot intended that the disclosure be limited to the specific examplesdisclosed.

EXAMPLES

Wafer bond/debond adhesives were characterized by using rheology tocharacterize the viscosity vs temperature of known good adhesives. Thisrheological analysis technique was used to determine that Phenoxyresins, a family of Bisphenol A/epichlorohydrin linear polymersavailable from InChem Corp NC, are useful as low cost,lower-temperature-than-polyimide bonding/debonding adhesives. FIG. 7 isa plot illustrating the viscosity of typical adhesives, such aspolyimide adhesives, as a function of temperature. A parallel platerheology technique used to analyze the complex viscosity vs temperatureof two TOK company adhesives and one brewer science adhesive. Plot line101 is data measured from an adhesive having tradename TMPR A0006, andplot line 102 is data measured from an adhesive having tradename TMPRA0206 both available from Tokyo Ohka Kogyo Co. (TOK Co), and bothbelieved to be examples of poly(meth)acrylates. Plot line 103 is datataken from a sample of tradename CR206, which is available from BrewerScience, and is also considered to be a poly(meth)acrylate. Referring toFIG. 7, at temperatures above 170° C. the viscosity of the samplesprovided by TMPR A0006, TMPR A0206 and CR206 decreases to the point thatreliable measurements of the viscosity can no longer be recorded.

The rheological analysis techniques that provided the data in FIG. 7where also applied to Phenoxy resins having different molecular weights.Phenoxy Resins where provided by resins having the tradenames PKHC®,PKHH® and PKHJ®, which are available from InChem Corp. Measurements ofthe viscosity as a function of temperature where taken from the phenoxyresins and the above described poly(meth)acrylate resins and plotted inFIG. 8 and FIG. 9. FIG. 8 is a plot illustrating a comparison of theviscosity of adhesives containing phenoxy resin in comparison topoly(meth)acrylate adhesives over a temperature range of approximately160° C. to 210° C. Plot line 201 is a measurement of viscosity for PKHH®Phenoxy Resin. Plot line 202 is a measurement of viscosity for PKHJ®Phenoxy Resin. Plot line 203 is a measurement of viscosity for PKCP-80®Phenoxy Resin. Plot line 204 is a measurement of viscosity for PKHC-80®Phenoxy Resin. Plot line 205 is data measured from an adhesive havingtradename TMPR A0006, and plot line 206 is data measured from anadhesive having tradename TMPR A0206.

FIG. 8 illustrates that Phenoxy PKHC® grade has approximately theViscosity response as the TOK adhesives ‘highest’ gradepoly(meth)acrylate adhesive, i.e., TMPR A0206, while the PKHH® grade ofPhenoxy resin provides significantly higher viscosities at temperaturesgreater than 170° C. PKHC® and PKHJ® grades of Phenoxy resin providedessentially the same viscosity performance in response to temperaturechanges.

FIG. 9 is a plot illustrating a comparison of the viscosity of adhesivescontaining phenoxy resin in comparison to poly(meth)acrylate adhesivesover a temperature range of approximately 40° C. to 210° C. Plot line301 is data measured from an adhesive having tradename TMPR A0006, andplot line 302 is data measured from an adhesive having tradename TMPRA0206, which are available from TOK Co. Plot line 303 is data taken froman adhesive sample of tradename CR206, which are available from BrewerScience. Plot line 304 is a measurement of viscosity for PKHC® PhenoxyResin of neat pellets. Plot line 305 is a measurement of viscosity forPKHJ® Phenoxy Resin. Plot line 306 is a measurement of viscosity forPKHC-80® Phenoxy Resin.

The data plotted in FIGS. 8 and 9 illustrate shows that phenoxy graderesins, such as PKHC®, PKHH® and PKHJ®, have comparable viscosity rangeto that of the TOK poly(meth)acrylate adhesive formulations, i.e., TMPRA0006 and TMPR A0206, at lower temperatures than 170° C. and have higherviscosity in the temperature range that is greater than 170° C.temperature range.

While the present disclosure has been particularly shown and describedwith respect to preferred embodiments thereof, it will be understood bythose skilled in the art that the foregoing and other changes in formsand details may be made without departing from the spirit and scope ofthe present disclosure. It is therefore intended that the presentdisclosure not be limited to the exact forms and details described andillustrated, but fall within the scope of the appended claims.

What is claimed is:
 1. A method for forming a semiconductor devicecomprising: forming at least one semiconductor device on the frontsurface of a device wafer; bonding a handling wafer to a front surfaceof the device wafer with phenoxy resin; thinning the device wafer fromthe backside of the device wafer; removing the adhesive comprisingphenoxy by laser debonding with an excimer laser; and forminginterconnects to the at least one semiconductor device extending througha back side surface of the device wafer.
 2. The method of claim 1,wherein the handling wafer comprises glass.
 3. The method of claim 1,wherein the bonding of the handling wafer to the device wafer comprises:applying a layer of the adhesive of the phenoxy resin on the frontsurface of the device by spin on deposition; contacting the layer ofadhesive with the handling wafer; and curing the adhesive layer at atemperature less than 300° C.
 4. The method of claim 1, wherein thephenoxy resin comprisespolyoxy(2-hydrozy-1,3-propanediyl)oxy-1,4-phenylene(1-methylethylidene)-1,4-phenylene.5. The method of claim 1, wherein the phenoxy resin has a viscosityranging from 100-10,000 Pa·seconds at a temperature ranging from 160° C.to 210° C., and under a pressure of at least 1000 mbar per area of an 8inch wafer size for at least one of the device wafer and handling wafer.6. The method of claim 1, wherein the thinning the device wafercomprises planarization or chemical mechanical polishing.
 7. The methodof claim 6, device wafer is thinned to a thickness ranging from 5microns to 10 microns.
 8. The method of claim 1, wherein the penoxylresin has a molecular weight ranging from 43,000 to 57,000.
 9. Themethod of claim 1, wherein the laser debonding comprises a 200 nm or 308nm excimer laser.
 10. A method of adhesive bonding comprising bonding afirst substrate to a second substrate with an adhesive comprisingphenoxy resin, wherein the adhesive has a viscosity ranging from100-10,000 Pa·seconds at a temperature ranging from 150° C. to 250° C.11. The method of claim 10, wherein the phenoxy resin comprisespolyoxy(2-hydrozy-1,3-propanediyl)oxy-1,4-phenylene(1-methylethylidene)-1,4-phenylene.12. The method of claim 10, wherein the penoxyl resin has a molecularweight ranging from 43,000 to 57,000.
 13. The method of claim 10,wherein the phenoxy resin is cured at a temperature of less than 300° C.14. The method of claim 10, wherein the viscosity ranging from100-10,000 Pa·seconds at the temperature ranging from 160° C. to 210° C.is when the first and second substrate are under a pressure of at least1000 mbar per area of 8 inch.